I wouldn't be surprised if most of you gained 10-20% in gas mileage by religiously applying these.
First, brakes are the worst enemy to gas mileage. An ideal trip to work for me involves absolutely no brakes, and that's about 20 miles city and highway. Every time you hit the brakes, your car slows, and you have to use gas to get your car right back up to that speed eventually. Instead of using the brakes, plan ahead and just let off the gas pedal. Doing this causes your car to go into DFCO, which keeps the engine running but uses zero fuel. The idea is we can slow the same amount as with brakes, but can do it much longer by just letting off the gas earlier. This holds true for red lights, traffic, and any other expected slowing.
I generally let off the gas about 1/2 mile before the red lights. Everyone behind me gets mad, passes me, and then I sit right behind them after we all get stuck at the red light. You're a winner, good job you got past me! Anticipate where you'll need to slow down, and let off the gas instead of using the brakes.
Keep engine rpm low. Besides being quieter and smoother, lower rpm uses less gas. Shift your cars early, I typically shift mine at 2,000rpm. The people behind me get mad for accelerating so slow, they pass me winning the prize, and then we cruise at the same speed. If your car has the power and is a manual skip 2nd and 4th, just go 1-3-5(6). Unfortunately my daily driver doesn't (1991 BMW 525i). Believe it or not, throttle percentage doesn't really have an impact on gas mileage, so you can press the gas pedal. However be mindful of power enrichment, which is where a car goes rich during high throttle levels to cool the cylinders. We absolutely never want to go into power enrichment. Unfortunately it's extremely difficult to know when this is happening. But as long as you never go above 80% throttle you'll be fine.
On the highway, follow big cars. Semis are the best if you aren't in a hurry. Drafting works. Get right behind them as close as you dare, and sit there. Semis drive slower than traffic so they rarely have to brake, and generally use cruise control so they maintain steady speeds. Now we should use cruise control on flat, non mountainous or hilly roads, but if you drive well, you'll get better mileage off cruise control by drafting. Or draft with cruise if you can exactly match the speed. It's impossible though.
On hilly roads, let the vehicle slow on the uphill, then accelerate on the down hill. Say you want to average 60mph on a drive. Let the vehicle slow to 50 going up the hill, then go 70 on the way down the hill. Obviously cops and other people don't like this, but where you can do it it does help.
Raise your tire's air pressure. If you don't mind the harsher ride, and have good traction, you can run at your tire's max.
Down force is bad. If you are the serious gas mileager, you'll make plexiglass covers to block off the openings in your front grill during the colder weather. I have yet to do this, but I have considered it. You aren't going to overheat when it's 0 degrees outside. Plenty of cars have trouble even reaching operating temperature in extremely cold weather. VW did a test where they had a TDi go something like 6 hours before the t-stat even opened for the first time. So for the winter, use the covers to smoothly block off the radiator gaps, and all of the other gaps in the front end. Under-body trays are also very helpful for mileage. Just leave ports to get to your oil drain plug.
Weight is the enemy of everything good on a car. Acceleration, handling, stopping distance, gas mileage, everything is hurt by weight. Cut excess weight as you can. Small, light wheels are a good place to do this. I'm not going to go through every place you can cut weight, but there are a bunch. On the other hand though, if you're worried about safety then you want weight. In a crash, the bigger car always wins. I've never seen an F350 lose a crash with another car.
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